Objective To explore the effects of unmanned aerial vehicle (UAV) application of mepiquat chloride (DPC) on cotton growth, development and yield components.

Methods A two-factor split-plot experiment was designed. The main plots were DPC application times, i.e., 6 applications (T1) and 4 applications (T2); the subplots consisted of 5 application dosages: 174 g/hm² (C1), 261 g/hm² (C2), 348 g/hm² (C3), 435 g/hm² (C4) and 522 g/hm² (C5). The regulatory effects of DPC application times and dosages under full-period UAV chemical control on the growth, development and yield of machine-picked cotton were studied.

Results Compared with 4 applications, 6 applications increased the number of upper bolls, middle bolls and inner bolls by 223.56%, 26.55% and 10.08%, respectively. Applying DPC 4 times reduced production cost and slightly affected cotton fiber quality. Under the same application times, the dry matter accumulation in cotton stems and leaves at the initial flowering stage, early boll-setting stage and boll-opening stage first increased and then decreased with the increase of DPC dosage, and the proportion of reproductive organs showed a similar trend. Excessive DPC dosage inhibited the growth of outer bolls and pre-summer bolls.

Conclusion Under the experimental conditions, for UAV chemical control in Southern Xinjiang, the optimal dosage is obtained at 435 g/hm² with 6 applications, and 348 g/hm² with 4 applications.